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  • Print publication year: 2013
  • Online publication date: June 2013

5 - Ore deposits formed in sedimentary environments

Summary

Ore deposits form in sedimentary environments as a result of one of two generalised geological processes: either as a result of mineral precipitation from solution in surface waters, most commonly from sea water or lake waters; or as a result of physical accumulation of ore minerals during processes of sediment entrainment, transport and deposition. The theoretical backgrounds to ore formation through each of these two processes are discussed separately followed by detailed descriptions of some important deposit types formed through each process.

Chemical precipitation from surface waters (hydrogene deposits)

Compositions of surface waters and ore mineral precipitation

A chemical sedimentary ore is one in which the concentration of ore minerals accumulated as a result of precipitation from solutions at the Earth’s surface. All natural surface waters are multi-element solutions. Average seawater contains about 3.5 wt % salts, comprising of order weight per cent levels of Na and Cl, and tens to hundreds of ppm of a number of elements of economic interest (Figure 5.1).

Further readings
Morey, G. B. (1999). High-grade iron ore deposits of the Mesabi Range, Minnesota – Product of a continental scale Proterozoic ground-water flow system. Economic Geology 94, 133–141.
Morris, R. C. (1993). Genetic modelling for banded iron-formation of the Hamersley Group, Pilbara Craton, Western Australia. Precambrian Research 60, 243–286.
Morris, R. C. and Kneeshaw, M. (2011). Genesis modelling for the Hamersley BIF-hosted iron ores of Western Australia: a critical review. Australian Journal of Earth Sciences 58, 417–451.
Powell, C. M., Oliver, N. H. S., Li, Z. X., Martin, D. M. and Ronaszeki, J. (1999). Synorogenic hydrothermal origin for the giant Hamersley iron oxide ores. Geology 27, 175–178.
Taylor, D., Dalstra, H. J., Harding, A. E., Broadbent, C. G. and Barley, M. E. (2001). Genesis of high-grade hematite orebodies of the Hamersley province, Western Australia. Economic Geology 96, 837–873.
Filipelli, G. M. (2011). Phosphate rock formation and marine phosphorus geochemistry: The deep time perspective, Chemosphere 84, 759–766.
Saxton, J., Fralick, P., Panu, U. and Wallace, K. (2008). Density segregation of minerals during high-velocity transport over a rough bed: implication for the formation of placers. Economic Geology 103, 1657–1664.
Slingerland, R. and Smith, N. D. (1986). Occurrence and formation of water-laid placers, Annual Review of Earth and Planetary Science 14, 113–147.
Craw, D. (2010). Delayed accumulation of placers during exhumation of orogenic gold in southern New Zealand, Ore Geology Reviews 37, 224–235.
Craw, D., Youngson, J. H. and Koons, P. O. (1999). Gold dispersal and placer formation in an active oblique collisional mountain belt, Southern Alps, New Zealand. Economic Geology 94, 605–614.
Hughes, M. J., Phillips, G. N. and Carey, S. P. (2004). Giant placers of the Victorian Gold Province. Society of Economic Geologists Newsletter 56, 1–18.